1. Field of the Invention
The present invention relates to an SAR measuring apparatus for measuring a specific absorption rate (hereinafter referred to as an SAR) based on a near magnetic field, for use in a radio apparatus such as a portable telephone, a portable radio apparatus, or the like.
2. Description of the Related Art
In recent years, portable radio apparatuses such as portable telephones or the like have been widely used. Accompanying with this, influence of electromagnetic wave radiated from a portable radio apparatus exerted on human bodies has been emerged as a problem. An SAR has been used as a general one to provide an index for this influence. It is herein noted that SAR is an electric power absorbed into a unit mass as a consequence of the exposure of a living body of a human being or the like to an electromagnetic field and expressed by the following equation:SAR=(σE2)/ρ  (1).
In this equation, E [V/m] is an electric field intensity, a [S/m] is an electric conductivity of a biomedical tissue, and p [kg/m3] is a density of the biomedical tissue.
According to the SAR estimation method of the so-called electric field probe method as described in the “Specific absorption rate measuring method for portable telephone terminal and the like used beside human body temporal region” of the Telecommunications Technology Council Report of Japanese Ministry of Public Management, Home Affairs, Posts and Telecommunications, there is used a so-called human body phantom, which is a human body model of which the shape, the dimensions and the electrical characteristics of the head tissue are simulated for the human body. By using this human body phantom, SAR that will probably occur in the human body, is experimentally estimated, as disclosed in, for example, a first prior document of “Standard of specific absorption rate measurement method of portable radio terminal”, issued by Association of Radio Industries and Business in Japan, ARIB STB-T56 Ver.2.0, revised on Jan. 24, 2002.
With regard to the SAR, worldwide regulations are progressing, and therefore, SAR inspection is indispensable for the production process for a portable radio apparatus such as a portable telephone or the like. Accordingly, there has been demanded a method and an apparatus for carrying out this SAR inspection simply and promptly. Conventionally, as a simple SAR estimation method, a method for experimentally obtaining SAR by a magnetic field intensity H on the surface of a human body phantom is proposed in, for example, a second prior art document of N. Kuster et al., “Energy Absorption Mechanism by Biological Bodies in the Near Field of Dipole Antennas Above 300 MHz”, IEEE Transaction on Vehicular Technology, Vol. 41, No. 1, pp. 17-23, February 1992. According to this prior art method of the second prior art document, it has been confirmed that the relationship of the following equation has held with regard to the distribution of SARs generated on the surface of the human body:
 SAR∝H2  (2).
As a conventional SAR estimation method, a method for obtaining an SAR distribution by calculating a current distribution from an incident magnetic field on the surface of the human body phantom when an electromagnetic wave is radiated from an antenna is disclosed in, for example, the Japanese Patent No. 2790103. A magnetic field is detected by a magnetic field probe provided with a movement and rotation mechanism, then the current distribution of the antenna is estimated, and the SAR is estimated based on this current distribution.
In a practical SAR measurement, the measurement is required to be carried out on various kinds of conditions of the arrangement of a portable telephone with respect to the head portion of a human body phantom, the type and the state of arrangement of the antenna and so on, and the maximum value of the SARs of the measurement results under various kinds of conditions is estimated to be the SAR value of the portable telephone. Therefore, much time is required for the measurement of SAR. Even by the above-mentioned simple SAR measurement method, it is necessary to change the method of arranging the portable radio apparatus with respect to the human body phantom. Moreover, during the actual SAR measurement, the portable telephone is measured in such a state in which it is closely fit to the human body phantom. According to the method of the prior art example as disclosed in the Japanese Patent No. 2790103, the incident magnetic field is measured on the surface of the human body phantom, and therefore, magnetic field measurement with the portable telephone arranged in conformity to the actual SAR measurement cannot be performed. Therefore, it is impossible to perform the inspection of SAR of the portable telephone on a production line by using the prior art SAR measurement method and apparatus.
Moreover, judgment of the SAR quality of the manufactured portable telephone is made not by the peak value of the SAR distribution but by an average value in a cube centered about the peak value (hereinafter referred to as an average SAR). The object to be judged is this average SAR, and there has been such a problem that the average SAR has been required to be calculated by some means. It is to be noted that the average SAR is also called a “local SAR”.